1. Field of the Invention
The present invention relates to a wiring structure for a transmission line.
2. Description of the Related Art
A conventional wiring structure for a transmission line is disclosed, for example, in the Japanese Laid-open Patent Publication No 10-326783.
FIG. 12 is a perspective view showing the conventional wiring structure. As shown in FIG. 12, the wiring structure for the transmission line is provided with a ground conductor 101, and a signal line 103 disposed so as to face the ground conductor 101 through a dielectric layer 102. As to a surface 104 of the signal line 103 facing the ground conductor 102, the irregularity (unevenness) in the direction parallel to the transmission direction is smaller than the irregularity in the direction perpendicular to the transmission direction. The irregularity increases the surface area of the signal line 103 to effectively reduce its conductor loss due to the skin effect. Another wiring structure relating to the above-mentioned wiring structure is disclosed in the Japanese Laid-open Patent Publication No. 9-36111.
In the conventional wiring structure for the transmission line, the conductor loss due to the skin effect can be effectively reduced by providing the irregularity on the surface 104 of the signal line 103 facing the ground conductor 101. However, the electromagnetic field generated between the signal line 103 and the ground conductor 101 may easily spread out due to the function of the convex portions in the irregularity at the end portion of the surface 104 of the signal line 103 facing to the ground conductor 101. The electromagnetic field causes electromagnetic induction in other signal lines adjacent to the signal line 103. Thus, there may occur such a problem that the wave shapes of the signals in the adjacent signal lines, in which the electromagnetic induction has been caused, are distorted.